Ultrasound (US) imaging systems have provided useful information about the interior characteristics of a subject under examination. An US imaging system has included a console and a probe that houses a transducer array. The transducer array has been electrically connected to the console via one coaxial cable per element or group of elements of the transducer array. Unfortunately, such a configuration is not well-suited for high channel count systems (e.g., 3D), wireless transducers, and/or other systems in which larger amounts of data are conveyed from the transducer array to the console.
A beamformer with a Sigma-Delta (ΔΣ) modulator can be used to reduce the amount of data transmitted between the transducer array and the console by digitizing the analog data from the individual channels, summing the digitized data into a single bit stream. Sigma-Delta modulation is discussed in Inose, et al., “A telemetering system by code modulation—ΔΣ-modulation,” Space Electronics and Telemetry IRE Transactions on SET-8(3), 204-209 (1962), and Sigma-Delta beamforming is discussed in U.S. Pat. No. 5,203,335 to Noujaim et al. and in U.S. Pat. No. 5,964,708 and U.S. Pat. No. 6,208,189 to Freeman et al.
Sigma-Delta beamformers have been targeted towards line-by-line beamforming, which requires dynamic focusing in receive (equivalent to variation of the delays between the contributing channels). U.S. Pat. No. 5,964,708 and U.S. Pat. No. 6,208,189 discloses a ΔΣ beamformer that utilizes a switchable feedback amplitude to compensate for errors introduced by dynamic focusing. This includes compensating for shortening the bit stream due to dropping samples out and stretching the bit stream due to adding samples. Unfortunately, these Sigma-Delta beamformers do not provide an output signal that is well-suited for high-quality imaging applications.